Candidate Electromagnetic Counterpart to the Binary Black Hole Merger Gravitational-Wave Event S190521g

We report the first plausible optical electromagnetic counterpart to a (candidate) binary black hole merger. Detected by the Zwicky Transient Facility, the electromagnetic flare is consistent with expectations for a kicked binary black hole merger in the accretion disk of an active galactic nucleus [B. McKernan, K. E. S. Ford, I. Bartos et al., Astrophys. J. Lett. 884, L50 (2019)AJLEEY2041-821310.3847/2041-8213/ab4886] and is unlikely [<O(0.01%))] due to intrinsic variability of this source. The lack of color evolution implies that it is not a supernova and instead is strongly suggestive of a constant temperature shock. Other false-positive events, such as microlensing or a tidal disruption event, are ruled out or constrained to be <O(0.1%). If the flare is associated with S190521g, we find plausible values of total mass M_{BBH}∼100  M_{⊙}, kick velocity v_{k}∼200  km s^{-1} at θ∼60° in a disk with aspect ratio H/a∼0.01 (i.e., disk height H at radius a) and gas density ρ∼10^{-10}  g cm^{-3}. The merger could have occurred at a disk migration trap (a∼700r_{g}; r_{g}≡GM_{SMBH}/c^{2}, where M_{SMBH} is the mass of the active galactic nucleus supermassive black hole). The combination of parameters implies a significant spin for at least one of the black holes in S190521g. The timing of our spectroscopy prevents useful constraints on broad-line asymmetry due to an off-center flare. We predict a repeat flare in this source due to a reencountering with the disk in ∼1.6  yr(M_{SMBH}/10^{8}  M_{⊙})(a/10^{3}r_{g})^{3/2}.

Characterisation of an antibody coated microcantilever as a potential immuno-based biosensor

In this study, we investigated the activity, stability, lifetime and re-usability of monoclonal antibodies to myoglobin covalently immobilised onto microfabricated cantilever surfaces. These sensing surfaces are of interest to us in the development of novel cantilever-based immunosensors. For such sensors the antibody layer represents the sensing element while the microcantilever acts as a mechanical transducer. A procedure for producing re-usable biological coatings has been tested with different independent techniques. An Enzyme Linked Immunosorbent Assay (ELISA) was used to determine the presence of an active antibody coating, and to monitor the lifetime and stability of the immobilised antibody. Through this analysis, the activity of the immobilised antibody layer was found to be more stable with the introduction of sucrose, as a stabilising agent. Sucrose was applied to the immobilised antibody layer after each regeneration step. The immobilised antibody was found to have a stable active lifetime for up to 7 weeks. Fluorescence microscopy was used to give information on the distribution of the coating on the gold and silicon nitride sides of the cantilever. Atomic Force Microscopy was used to determine the presence of the biological coating on the cantilever and to obtain information on the surface morphology of the biological element of the sensor. The combined results provide valuable information on the development of an optimised sensing element and demonstrate a set of methods to use for future sensor-to-sensor characterisation. Preliminary experimental results showing the antibody activity against myoglobin, detected with a microcantilever based sensor prototype confirmed the motivations and potentialities of the proposed immunosensing technique.

The direct calculation of parametric images from dynamic PET data using maximum-likelihood iterative reconstruction

The aim of this work is to calculate, directly from projection data, concise images characterizing the spatial and temporal distribution of labelled compounds from dynamic PET data. Conventionally, image reconstruction and the calculation of parametric images are performed sequentially. By combining the two processes, low-noise parametric images are obtained, using a computationally feasible parametric iterative reconstruction (PIR) algorithm. PIR is performed by restricting the pixel time-activity curves to a positive linear sum of predefined time characteristics. The weights in this sum are then calculated directly from the PET projection data, using an iterative algorithm based on a maximum-likelihood iterative algorithm commonly used for tomographic reconstruction. The ability of the algorithm to extract known kinetic components from the raw data is assessed, using data from both a phantom experiment and clinical studies. The calculated parametric images indicate differential kinetic behaviour and have been used to aid in the identification of tissues which exhibit differences in the handling of labelled compounds. These parametric images should be helpful in defining regions of interest with similar functional behaviour, and with FDG Patlak analysis.

Noninvasive quantification of rCBF using positron emission tomography

This study proposes a new method for the pixel-by-pixel quantification of regional CBF (rCBF) with positron emission tomography and H(15)(2)O by using a reference tissue region. No arterial blood is required. Simulation studies revealed that the calculation of rCBF was fairly stable provided that the frame time was relatively short compared with total scan time. In practice, calculated CBF images correlated significantly with those obtained with the dynamic/integral method. Because the method accurately detects changes in CBF, it is particularly suitable for brain activation studies.